Among lead-acid storage batteries used in various fields such as automobiles, there is one including positive electrode plates and negative electrode plates layered alternately with separators interposed therebetween in a container. There is a lead-acid storage battery as disclosed in JP-A-2004-311357, in which a separator protrudes farther than outer peripheral edges of plates in order to prevent a short circuit caused by elongation of the positive electrode plate.
However, the lead-acid storage battery in JP-A-2004-311357 is still susceptible to improvement in prevention of the short circuit between the positive electrode plate and the negative electrode plate due to elongation of the positive electrode plate. Moreover, if the plates deteriorate and active materials fall on the fallen active materials may cause a short circuit between the positive electrode plate and the negative electrode plate. Specifically the fallen active materials accumulate between end portions of the separator and inner walls of the container to cause the short circuit between the positive electrode plate and the negative electrode plate.